The subject matter disclosed herein relates to impact test fixtures. More specifically, the subject disclosure relates to impact test fixtures for rotating hardware.
Rotating components, for example, helicopter rotor blades, are exposed to impact with birds, shed ice, objects on the ground and the like. Testing performed to demonstrate compliance with impact requirements is typically performed on a rotating blade assembly because the force of the impact on the rotor blades is dependent on the natural frequencies of the blade. These natural frequencies depend on the blade mass and the stiffness of the blade which itself is dependent on centrifugal force generated by the rotating blade. Spinning the rotor blade accurately produces the necessary centrifugal force, but such a test is expensive and properly timing the projectile to impact the desired location on the spinning blade is difficult.
Prior art fixtures have utilized cables, pulleys and/or springs connected to a reinforced portion of the blade which pull the blade radially in an attempt to replicate centrifugal forces in a stationary blade. The reinforcement typically includes a laminate buildup on an outboard section of the blade and a cuff bolted thereto to which the cable or other pulling means would be attached. This configuration adds significant weight to the outboard end of the blade which reduces the natural frequency of the blade resulting in an un-conservative reduction in the force of impact. The art would well-receive improved testing fixtures and methods which would accurately replicate the centrifugal force while reducing the effects of the fixtures on the impact force resulting from the test.